Recent studies published in the journal reveal that Uranus emits approximately 15% more energy than it receives from the Sun, as documented in Monthly Notices from the Royal Astronomical Society and Geophysical Research Book.
Composite image of Uranus. Image credit: Marcos Van Dam/Wm Keck Observatory.
Uranus distinguishes itself from other planets in our solar system by rotating on its side, causing each pole to face the Sun for 42 consecutive years during its “summer.”
This planet also rotates in a direction opposite to all other planets except Venus.
Data from the 1986 Voyager 2 flyby mission showed that Uranus has an unusually cold interior, prompting scientists to reconsider how the planet formed and its evolution within the solar system.
“Since the Voyager 2 flyby, there’s been an assumption that Uranus lacks internal heat,” said Dr. Amy Simon, a planetary scientist and co-author from NASA’s Goddard Space Flight Center. First paper.
“However, explaining this has been challenging, particularly when compared to other giant planets.”
“The data regarding Uranus’s heat emissions originated from a single measurement made during the Voyager 2 mission,” Dr. Simon noted. “This reliance on one data point created a significant challenge.”
Through advanced computer modeling and analysis of decades of data, Dr. Simon and her colleagues discovered that Uranus does, in fact, generate internal heat.
To understand a planet’s internal heat, scientists compare the energy it receives from the Sun to the energy it radiates back into space as reflected light and emitted heat.
Other giant planets like Saturn, Jupiter, and Neptune emit more heat than they receive, suggesting that the excess heat originates from within.
The rate at which a planet releases heat can indicate its age; a planet that emits less heat than it absorbs is generally considered older.
Because Uranus was believed to emit an equal amount of heat to what it received, it was initially thought to lack internal heat.
This discrepancy puzzled scientists, leading them to speculate that Uranus might be significantly older than its neighbors, having completely cooled over time.
Some hypotheses suggested that a massive impact (possibly the same event that tilted the planet) may have stripped Uranus of its internal heat.
However, these theories did not satisfy researchers, motivating them to investigate what they termed the “Uranus cold case.”
“Did we mistakenly believe that Uranus has no internal heat?” asked Professor Patrick Irwin from Oxford University, the lead author of the first paper.
“We conducted extensive calculations to evaluate how much sunlight is reflected by Uranus, only to realize that it is actually more reflective than previously estimated.”
Researchers aimed to assess Uranus’s overall energy budget, exploring the total energy received from the Sun, the light reflected, and the heat emitted.
This required calculating the total light reflected from the planet from various angles.
“We need to consider light scattered across the planet’s surface instead of just direct reflections,” Dr. Simon explained.
To provide the most accurate energy budget estimate for Uranus, scientists created a computer model incorporating all available data on Uranus’s atmosphere from decades of ground- and space-based observations, including data from the NASA/ESA Hubble Space Telescope and NASA’s infrared telescope in Hawaii.
This model accounts for factors like haze, cloud cover, and seasonal changes that influence how sunlight is reflected and heat escapes.
The findings reveal that Uranus emits about 15% more energy than it receives from the Sun, as reported in a second study.
These investigations suggest that Uranus possesses its own internal heat but emits more than twice the energy it receives, although still less than its neighbor, Neptune.
“Now we need to delve deeper into what the additional heat on Uranus signifies and improve our measurement techniques,” Dr. Simon concluded.
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Patrick GJ Irwin et al. 2025. Uranus’ bolometric binding albedo and energy balance. mnras 540(2): 1719-1729; doi: 10.1093/mnras/staf800
XINYUE WANG et al. 2025. Uranus’ internal heat flux and energy imbalance. Geophysical Research Book 52 (14): E2025GL115660; doi: 10.1029/2025GL115660
Source: www.sci.news
